A Deadly Doctor, simply put, is someone who fights or kills with a medical motif. He uses his medical knowledge to injure, torture or kill, and uses syringes, pills or surgical instruments or medical techniques to achieve his goals. Surely the ultimate example of the Morally-Ambiguous Doctorate. One reason for this is due to all his/her training: while having advanced knowledge on the human body can be used to save people, it also gives all the knowledge on how to injure and kill people with minimal effort by knowing all the body's weak points.

Note that this trope is not "Any doctor who is a good fighter." That would be Combat Medic. Deadly Doctor refers specifically to doctors who apply their medical knowledge to their combat techniques.

A subtrope of Mad Doctor. Compare Depraved Dentist. Contrast Martial Medic, a character who heals with knowledge they gained in the course of learning to injure people. And while people tend to die around him (not his fault, we assure you), The Doctor is not one of these.

Examples of Deadly Doctor include:

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One of the earliest anime/manga examples is Black Jack, who was known not only as a superhuman surgeon but as a deadly marksman who could kill or, more commonly, incapacitate enemies by throwing scalpels.

Dr. Shamal from Katekyo Hitman Reborn is a doctor/assassin who kills people by infecting them with terminal illnesses from his special mosquitoes.

Catherine from Gregory Horror Show. She is a nurse with a blood-taking fetish and a syringe as big as she is.

Tony Tony Chopper of One Piece isn't particularly malicious, so the largest extent he's really used his medical knowledge to fight is through a special medicine that improves his shapeshifting abilities, and by pointing out the weak spots of a zombie, since it was already dead. Doc Q, aptly nicknamed 'Grim Reaper', of Blackbeard's crew seems to be a straighter example, though we haven't seen him do all that much just yet.

You know, besides handing out apples with bombs in them, for giggles. But not any actual doctoring, not yet anyway.

Then there's Trafalgar Law, also known as "The Surgeon Of Death." Which is...odd, to say the least, looking at him. He has the power of the Op-Op Fruit, which allows him to perform spontaneous operations (hence the name) on anyone or anything sufficiently close to him. He uses his medical knowledge to inflict whatever effects he wants with minimum effort. Also, he carries around a greatsword as his scalpel.

Dr. Muraki from Descendants of Darkness. In the first volume of the manga alone, he turns a dying girl into a vampire and controls her in order to kill people, captures a shinigami and tortures/basically tries to dissect him, and then faces off with Tsuzuki, known as the most powerful of the shinigami, breaking Tsuzuki's spine at one point and escaping at the end of the book. His skill and knowledge as a medical doctor assist him in his various evil endeavors.

Nurse Witch Komugi is a medical-themed Magical Girl. She started as Komugi Nakahara, a deranged mutant nurse with a fetish for oversized medical equipment (especially needles) in the much darker anime The SoulTaker.

Minoru "Doctor" Kamiya of Yu Yu Hakusho fights with hands that cut like scalpels, and insects with syringes that inject diseases into his victims.

Yusuke is highly resistant to killing Doctor even though he's in some ways the most horrifically evil person he's yet faced. Ultimately he does not do so, though there's some Deus Ex Genkai involved. The Fridge Logic of this, when Yusuke's been killing sentient demons since his first case, hits in a sneaky way after the end of the Sensui arc.

I.e., Yusuke's stand on "to you, people is food" appears to have gotten a little...warped in the aftermath of turning into a demon. Sanada-san informs him he freaks her out and should leave the world now on overhearing the first manifestation of this. While it has a few later appearances, it is never discussed again.

Fantastic Racism plays an important and weird part in the whole series. Togashi attempts a hasty resolution at the end that makes no sense at all.

Naruto has Kabuto, who uses the medical knowledge he picked up as a longtime mole to do incredible damage to others' bodies.

And then we have Sakura Haruno, the seemingly harmless kunoichi, but lo if you piss her off or on the wrong side of the battlefield, for she has a punch that can send large boulders flying from the ground.

Keep in mind she learned both healing and those punches from Tsunade, who was the leader to a large village of ninjas. Tsunade is still way stronger and a much better healer.

Rosario + Vampire has one of the hybrids posing as a nurse. She can control her victims with some kind of poison.

Higurashi no Naku Koro ni has plenty of perfectly nice people infected with the Hate Plague and killing one another in various disturbing ways, but nurse Takano Miyo always seems to be the first to go. Still, further and further into the show, she seems just as creepy as the crazy person of the month if not more so. Then comes The Reveal, in which she engineered the whole thing and plans to slaughter the whole town and turn over the virus to military researchers who could use a squad of paranoid people willing to listen to lies and kill their friends...

Faust VIII from Shaman King. He could use his medical knowledge to take down enemies and even survive falling out of a plane in a wheelchair without a parachute.

Although considering he's a necromancer, it may be he his body is mostly dead anyway and he simply needed to locate any lost limbs after landing.

In Steam Detectives, the black-clad nurse Lang-Lang who serves Boy Criminal Le Bledd the same way the white-clad nurse Ling-Ling serves Boy Detective Narutaki, the hero of the series. Lang-Lang began trying to heal people, but decided it was easier to end their suffering by killing them; she likes the idea of preserving handsome young men/cute boys via taxidermy "so they stay young for ever!" Oh, and she is Ling-Ling's sister, though not an actual twin...

Palparepa, the Big Bad of Gao Gai Gar FINAL, was a clinically white doctor with giant syringes sticking out the back of his mech. He uses them to upgrade himself by sticking his mech with them, a move named "Doping Cylinder". It's appropriate for a show where the villains' gimmick is super regeneration and The Hero is the "God of Destruction".

The school nurse from Yu-Gi-Oh GX is a pretty decent girl and an excellent healer, normally, but after she's turned into a Duel Ghoul in the first half of the third season, it's revealed she has a deck that caters to this theme, giving you life points while using cards that turn that gain into damage. Not surprisingly, her key card in that deck is a demonic nurse wrapped in bandages.

Kuroudo Akabane aka. Dr. Jackal from GetBackers, who was once a medical doctor tasked with saving lives, but after letting a child die on his watch, decides that he's probably better off mutilating and killing people instead.

Sanada Kazuki: Chick Magnet, genius, and mild-mannered heir to a not-so-mild fortune. Did I leave anything out? Well, he is the one-time national boxing champion and successor to the Hama school of fisticuffs. His style involves rapid calculation of body strength, stun duration, and vulnerable organs and nerve clusters, reforminghim into something of a Badass Bookworm in the ring.

Medusa can technically count, too, since she took a brief residency as the DWMA's head nurse.

One Monster of the Week of Yuugen Kaisha is a doctor who made a Deal with the Devil so he can murder patients and harvest their organs for sale (magically concealing the evidence). He got some sort of demonically-possessed superpowers as part of the bargain as well, and tosses scalpels and manipulates a laser surgery machine telekinetically, or as the dub has it:

Lieutenant Karion: Psychokinesis?Ayaka Kisaragi: Or just psycho!

The manga, "Eliminate Dangerous Doctors" or EDD is basically this trope being hunted down by a secret agency (which itself may not be as well-intenioned as it may seem, making this a case of Black and Gray Morality with the unlucky only good doctor protagonist thrown into the situation).

Not to mention Dr. Moon, who considers himself an artist when it comes to pain. He's also a self-taught medical genius who uses his incredible talent to cause suffering rather than heal.

Even heroes with medical doctorates have been known to use their skills to incapacitate people.

Ratchet, in the Transformers: Shattered Glass universe. Being in his care is more of a punishment than a treatment, as he tends to whimsically replace his patients' body parts with whatever he thinks would look better.

Hush of the Batman comics evolves into this after he drops the guntoting. Scarecrow also counts, having been the head psychiatrist at Arkham.

Haku in the Naruto fanfic Hakumei. After apprenticing to a medic-nin for some years, his fighting style incorporates drugs and poisons, and while he doesn't like hurting people, he's ruthless when he has to be. His friends would say that he's the scariest member of their group.

Winter War (a Bleach AU where Aizen won the war) has Ogidou, a former Fourth Division member who fights by reversing healing kidou. For example, one of his attacks reopens old wounds that have scarred over. The other members of La Résistance let him do it, but find it disturbing. Hinamori, who's part of the same small group of fighters, refuses to let him heal her, even though she acknowledges that he's competent.

Elle Driver disguised herself as a nurse in Kill Bill in order to carry out a hit on The Bride with a poison syringe, only to have her mission canceled by Bill himself. Since Elle despises the Bride, she does not take it well.

Repo the Genetic Opera has the Repo Men, trained medical professionals who mostly do their deadly work with scalpels, and the Genterns, who, while they don't kill people nearly as often, can be pretty damn sinister.

Ghostbusters: Egon Spengler states that Ivo Shandor, also the architect behind that building, was one of these.

Ton Phanan from the X-Wing series, who was a doctor before cybernetics ate his future and he became a pilot-medic. At one point he cuts a man's throat using a laser scalpel, and notes that anything in his medical kit can be weaponized.

Interrogating Colonel: "Did you surrender this weapon to our guards before coming before me?"Phanan: "What weapon, sir?"Interrogating Colonel: "The laser scalpel."Phanan: "Not a weapon, sir. It's a tool of medicine. I wasn't asked to turn over my bandages, bacta treatments, disinfectant sprays, or tranquilizers either, but I can kill a man with any of them, under the right circumstances."

And Mij Gilamar, from the Republic Commando Series. His medical knowledge is considerable, but add to that the fact that he's the very definition of a Combat Medic, fully trained as a Mandalorian soldier, and you've got someone who can just as easily put you together as take you apart. Though normally a very kind, and even somewhat charming man, when asked about why he wears the Mandalorian color of vengeance on his armor, he has this to say:

Gilamar: "I fell in love with a Mandalorian girl, married into the clans, and a hut'uun killed her. I know his name. I'll find him. And then I'll show him what it means to make a bad enemy of a Mandalorian with anatomical expertise and a scalpel."

The Heralds of Valdemar series once states that the same Healers who can stop the pain and put you together also know how to take you apart, so it's unwise to anger them.

In the Sherlock Holmes short story "A Study in Emerald" by Neil Gaiman, the Great Detective remarks, concerning his deduced perpetrator of a brutal murder, "[I]t is my experience that when a Doctor goes to the bad, he is a fouler and darker creature than the worst cut-throat." Of course, the reader is more likely to agree with Dr. Watson on the rightness of his actions, making this a subversion.

The actual Sherlock Holmes said something to the same effect in 'The Adventure of the Speckled Band,' the same story in which he observed that the city might be full of horrors, but what people get up to in the privacy of the country really chills his blood.

The story in which Holmes explains how crime can be committed with impunity in the country is actually "The Adventure of the Copper Beeches," though the "A Study in Emerald" quote is inspired by Holmes calling a doctor "who goes wrong" the "first of criminals" in "The Adventure of the Speckled Band".

Watson might also be considered a Badass Doctor. Holmes frequently asks Watson to bring his revolver along on investigations that may become dangerous, he was a doctor in the war and was wounded in Afghanistan, and still goes on these various risky adventures despite the fact that his wound sometimes still bothers him.

Which makes him a Martial Medic. And though he certainly has the capacity to be a Deadly Doctor, he's more a Combat Pragmatist - for example, see how he's ready to bash a chair over the head of Charles Augustus Milverton in the canon.

In "Melanie and Merrick", Nurse Katie Heller, who has Manchausen Syndrome by Proxy, uses her medical knowledge of medicines to kill off patients, sometimes even swapping their prescribed medicine with a deadly substance. Her ultimate plan to kill off the Elephant Man fails heavily, and her ass is kicked hard by the hospital's scrubber, Melanie Bell. Naturally, Katie is fired.

In The Father Luke Wolfe Trilogy, Dr. Brandt scratches Father Wolfe's wrist with a nicotine-filled syringe as a "reminder" to give his son a passing grade. He also threatens that worse than nicotine would have been an empty syringe, since a bubble of air in the bloodstream can jolt the heart into stopping. It turns out this is how he murdered his colleague earlier.

In Aaron Allston's Galatea in 2-D, Medea was designed for this. She both designs the poison to use on Red, and its antidote. And it is Roger, not Medea, who has scruples about it.

A Monster of the Week on Charmed is Doctor Williamson, and infectious disease specialist who had treated Piper when she was sick a few episodes earlier. He's a good guy, but when he accidentally injects himself with Piper's blood, he also gets her powers. Turns out mortal + powers = CRAZY. He goes on a killing spree and takes organs from people. Piper eventually has to kill him to stop him, which she finds very hard to do, as he is the first human she ever killed, and he tried to save her life.

Dexter's first kill is of a homicidal nurse, who overdoses patients in her care that she considers to be in too much pain to keep living.

For that matter, Dexter himself attended med-school before becoming a blood spatter analyst. This explains his surgical killing style and familiarity with anatomy and pharmacology.

Subverted in Bakuryuu Sentai Abaranger. Dr. Yukito Sanjou/Abare Blue is a chiropractor who doesn't bring its expertise in battle, but when he actually does chiropracticing, it was extremely painful (though you'll feel better afterwards) that could make even battle-hardened veterans wince in pain. Then there's Dr. Mikoto Nakadai, who didn't quite bother bringing his medical expertise in battle or whatever, but considering his battlecapabilities, and his motivation... he's deadly on his own.

In the crossover with Ninpuu Sentai Hurricaneger, Yukito did use his chiropractor knowledge to crush the monster of the movie's bones... unmorphed(it's just a clone though)

CSI Doctor Jekyll. He used surgical means to kill his victims, like the guy who got an infected appendix sewn into him.

In the territory days, Dr. Sam Sheppard (who may or may not have inspired The Fugitive) became a wrestler in his later years, exploiting his extensive anatomical knowledge to great effect in the ring through the use of Pressure Points.

The Orks of Warhammer 40,000 have "Mad Doks" or "Painboyz" to keep the lads on their feet during battles, and who occasionally put their bonesaws and "'Urty Syringes" to offensive use (the latter is an actual piece of wargear that does poisoned attacks). Since the specialists in question are mad scientist-esque physicians with an instinctive (if imprecise) grasp of medicine and an urge to "tinker," they count as Deadly Doks off the battlefield, too.

The main job of Space Marine Apothecary is to keep their battle-brothers alive and collect the gene-seed of the dead, but being an 8-foot-tall genetically enhanced Super Soldiers in Powered Armour, they can and will kick ass if necessary. Not to mention that using the gene-seed extractor on a living person is going to hurt.

Combat-oriented clerics in Dungeons & Dragons. One can just imagine a death effect spell being the cleric carefully and precisely snipping off a few selected blood vessels in the target's brain.

Eberron's House Jorasco focuses on healing (and, thanks to the power of their Dragonmark, has managed to severely cut down the temples' share of the magical healing market), meaning an adventuring Heir would have some aspects of this trope by default. The Jorasco prestige class added by the Dragonmarked sourcebook fits it even better, as it models a secret sect within Jorasco that turns their healing powers to the art of diseases (as in, causing them) and harm. Given that they have to be non-good, the best case scenario is an Anti-Hero.

Surprisingly subverted by Yawgmoth in Magic the Gathering. Despite being the Big Bad, he was a very skilled doctor and, even if his cure for phthisis wasn't seen well, it actually worked. Even when he started adding massive doses of Body Horror, his target was always to improve his patients, not to murder them.

The Combat Medic in most class-based shooters such as Battlefield series, are given sufficient firepower to make sure they remain fun to play. In Bad Company 2, the medic class is the only one who gets machine guns.

In Knights of the Old Republic, the Heal Force power is closely related to the Wound power. Every Jedi in both games can end up with both.

The Medic in Team Fortress 2 can be pretty deadly with the bone saw if you can get close enough. Or his syringe gun.

He's got decent, self-regenerating health, a good running speed, has an alternate syringe gun that drains health, can heal at range, make his healing target and himself invulnerable, and has this [dead link] as his alternate bonesaw. Even his backstory as a psychotic Mad Scientist fits the bill. And then there's his TFC equivalent, who was more or less a full combat class with the ability to heal people.

To drive the point home, one of his melee weapons is a bust of Hippocrates' head with a "Do No Harm" plaque. Which he uses to beat people to death with.

It explains a lot about his personality and style that he was trained in medicine in a time and place where the Hippocratic oath was downgraded to a Hippocratic suggestion.

Various mercenaries in Jagged Alliance have medical diplomas and high medicine skill. They generally have lower marksmanship skill then professional soldiers, but have no restrictions against killing enemies. Many of them are expert melee combatants thanks to their familiarity with scalpels.

Conversely, the Healer character class in Nethack, while having mostly magical healing abilities, begins with a scalpel as their melee weapon.

But is also the best class available for pacifists.

Speaking of which: all of the nurses in Nethack will try to kill you. Unless you remove all armor and weapons, in which case they will raise your maximum HP instead.

Faust of Guilty Gear fame is a 9-foot-tall doctor who wields a scalpel as big as he is. Bonus points in that he actually heals people as well as kick ass, and kicks ass in order to stop people from getting hurt in the first place. Now that's what I call, aggressive vaccination.

He's strongly implied to be the same as Doctor Baldhead from the first game, who was... less nice. After he accidentally killed one of his patients, he snapped, and started wantonly killing people while under the delusion of treating them.

Kyoko Minazuki from the Rival Schools series, who serves as a school nurse when she's not cracking skulls.

Dr. Schabbs, the Episode 2 Final Boss in Wolfenstein 3D. He wore a lab coat and was armed with a needle filled with the "poisonous corpsokinetic animation serum" he used to create his mutant zombie soldiers.

How is it that Wilhelm "Deathshead" Strasse of Return to Castle Wolfenstein fame is not here?

Dr. Vahzilok from City of Heroes, who uses his modern scientific equipment to conduct strange, forbidden experiments... on himself as well as others.

In the Fallout games, there is a perk which gives you a bonus to medical skills, but also, due to your mastery of anatomy, raises your base damage.

More of an example being your Father in Fallout 3: He just, on a whim, decides to escape a secure vault, cross the wasteland from one side to the other with no companions (a feat replicated only by your stupidly powerful character) and no arnament except a hunting rifle. He then proceeds to enter and leave a super-mutant infested building (unwounded!) and then a mind-control simulation pod before he calmly sacrifices himself in an attempt to wipe out the leader of the Enclave assault on the Capital Wasteland. He is a Badass doctor like no other.

Mordin Solus from Mass Effect 2 averts the trope. He's an extremely skilled doctor as well as a complete Badass, but he'd never kill anyone with medicine. Nonetheless, while people are thankful for his medicinal work, the fact that he takes lives as easily as he saves them utterly terrifies more than a few who know of him.

Played with; the fact that he was part of the STG team that developed and deployed the second version of the genophage gnaws his conscience hard. He tries hard to justify his actions, but millions of unborn krogan children and the cultural and emotional heavy decay the krogan, as a race, suffer are a heavy burden to carry, as Maelon wisely points. And it's a major plot point on his character development.

"Have killed many people, Shepard. Many methods. Gunfire, knives, drugs, tech attacks. Once with farming equipment. But not with medicine."
"Many ways to help people. Sometimes cure patients. Sometimes kill dangerous people. Either way helps."

A large amount of modern MMORPGs that have a healer class archetype will allow, to greater or lesser extent, the player to choose skills, stats and/or gear to make them more offensive than defensive. Whilst a viable tactic in most cases, there will always be fallout from the... "purists" who will insist that healers heal and that anyone not playing them straight is a Scrub and wasting the time of all concerned. Potentially the basis for realtime FlameWars.

The Etrian Odyssey series' Medics can be powerful front-line fighters, the exact opposite of their intended role as fragile healers. This requires very deliberate skill-tree set ups but is surprisingly practical.

In addition, both of the healing classes in Etrian Odyssey III, the Prince(ss) and the Monk, have fairly potent combat ability, especially the Monk, and especially once you unlock subclassing.

Dr. Litchi Faye-Ling in BlazBlue is another aversion. She's a clear doctor and helps in healing people, but she never brings her medical knowledge in combat, and usually fights with telekinesis, chi control and martial arts... nor did she specifically target some body parts for medical damage.

Hatoful Boyfriend has Dr. Iwamine Shuu, the school doctor at St. PigeoNation's School. He is so deadly that he may cut off your head, and possible also study your insides most intimately once he's done with your pretty head.

Skullgirls has Valentine, who fights with medical equipment such as bonesaws, syringes, IV stands, and more.

You could consider Shadow Naoto from Persona 4 this. After all, she was going to medically change Naoto's gender. That said, she's also a bit of an aversion. She fights with the usual magic powers and technology, no real use of any sort of medical knowledge.

In The Adventures of Dr. McNinja, Dr. McNinja, who fights in medical garb (but does so with standard ninja weapons). Played straight only once, when he had to defend himself with nothing but his stethoscope. It's broadly hinted that, while he is strong and stealthy because he's a ninja, what really makes him dangerous is his intimate knowledge of human anatomy.

Dr. Zexion of Ansem Retort. Granted he doesn't fight with a medical motif, but he is a heartless killer, so he counts.

He may not fight with a medical motif, but he certainly kills (and injures, and maims, and mutates) with one. Case in point: Riku's liver. Firecracker. Surgical implantation.

The Nazis were known for terrible experiments performed on live people including vivisection. Josef Mengele was one of their more infamous doctors.

Also, the Imperial Japanese Army. A lot of their doctors escaped punishment for war crimes in exchange for handing over their research data to the Americans.

Jack the Ripper was speculated to have possibly been a professional surgeon or doctor due to the nature of the cuts/incisions on some of his victims.

While he never killed anyone or even practiced medicine, Japanese surrealist writer Kobo Abe did not do well in his medical studies, and was awarded his degree on the condition that he never practice. Jokes have been made that considering his genre and the content of his stories, it's probably for the best.

Hippocrates intended to avert this trope by making his students swear not to teach medicine to anyone who wouldn't take the Oath. The Hippocratic Oath expressly forbids the use of the medical arts for destructive or exploitative ends.